Convert Lines per millimetre to Lines per inch

Convert Lines per millimetre (lp/mm) to Lines per inch (lpi) instantly and accurately.

Conversion Formula

lpi = lp/mm × 25.4

About Lines per millimetre

The line pair per millimetre (lp/mm) is the fundamental unit of spatial resolution in classical optics, characterising the resolving power of a lens, film emulsion, sensor, or microscope objective. A resolving power of N lp/mm means adjacent line pairs separated by 1/(2N) mm can be distinguished - derived from the Abbe diffraction limit (Ernst Abbe, 1873) and Rayleigh criterion (Lord Rayleigh, 1879). Film benchmarks at MTF50: Kodak Tri-X 400: 63 lp/mm; Fujifilm Velvia 50: 160 lp/mm; Kodak Technical Pan: 320 lp/mm. Lens benchmarks: Leica APO-Summicron-M 50 mm f/2 ASPH: ≈ 75 lp/mm at centre. CMOS sensor Nyquist frequency: for pixel pitch p mm, f_Nyquist = 1/(2p) lp/mm - a 4.63 µm pixel limits at ≈ 108 lp/mm. As a dimensional unit, 1 lp/mm = 25.4 LPI = 25.4 PPI exactly. 1 lp/mm = 25.4 PPI.

About Lines per inch

The line per inch (lpi) is the standard unit of halftone screen frequency in offset, flexographic, gravure, and screen printing. Each halftone cell varies in dot size to simulate grey tones; a 150 lpi screen on a 1200 DPI printer allocates 1200/150 = 8 printer dots per cell row, giving an 8×8 = 64-level grey matrix. Industry benchmarks: newsprint 85-100 lpi; magazines 133-175 lpi; fine-art offset 175-200 lpi; screen printing (textiles) 35-65 lpi. Rule of thumb: required DPI ≥ 1.5 × lpi for acceptable AM halftone; ≥ 2 × lpi for high quality - so 150 lpi offset needs at least 300 DPI raster data. As a dimensional quantity, 1 lpi = 1 PPI = 1 DPI; lpi designates screen frequency in print. 1 lpi = 1 PPI = 2.54 lpcm.

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